Display apparatus for displaying an image representative of an interlaced video signal

ABSTRACT

A display apparatus includes means for inputting an interlaced video signal comprising signals representative of successive fields in image data produced by scanning successive image frames. Fields of image data that have been derived from single frames of the scanned image frames are determined, and signals produced representative of each of the image frames. A DMD for each color channel is addressed with signals representative of the frames.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to display apparatus. In particular the inventionrelates to display apparatus in which an interlaced scan video signalderived from a film source, using for example a telecine scanner, isused to address a progressively scanned spatial light modulator, forexample an array of electrically deflectable mirrors. Such an array ofmirrors is commonly known, when addressed with digital signals as adigital mirror device, but is also referred to as a deformable ordeflectable mirror device, or DMD.

The video signals conforming to most transmission standards, includingthe PAL, NTSC and SECAM standards, are formatted in an interlaced scanmode intended for use with a scanned display system, for example adisplay system using a cathode ray tube such as in domestic televisionsystems or in some projector systems. To produce such interlaced videosignals, each image frame is divided into two fields, the first field ofeach image frame being designated an “odd” field and comprising all theodd numbered horizontal lines scanned across the image frame, and thesecond field being designated an “even” field and comprising all theeven numbered lines. When the video signal is used to drive a scanneddisplay system such as a television receiver, the two fields of eachframe are displayed in the same sequence in which they were recorded,and are integrated by the eyes of the observer who will observe thereconstituted image frame.

Digital mirror devices comprise an array of deflectable mirror elements,each mirror element including a mirror surface mounted on a torsionelement over a control electrode. Applying an electrical potential toeach control electrode causes the associated mirror surface to pivot,thus changing the direction of light reflected from the mirror element.By application of suitable electrical address signals to the digitalmirror device, selected mirror elements will reflect light in either an“on” direction towards a projector lens for projection onto a displayscreen, or an “off” direction towards a beam dump. It is thus possibleto spatially modulate a beam of light incident on the digital mirrordevice to produce a projected image on a display screen. The pixels ofthe image displayed on the display screen will be produced by lightreflected from one or more of the mirror elements.

Unlike cathode ray tube based systems such as television receivers whichuse such interlaced address signals, display systems using digitalmirror devices display a full frame of information every field interval,all the pixels representing the frame being illuminated simultaneouslyrather than scanned as in a cathode ray tube. In its simplest form, eachpair of successive fields may be combined to produce a complete framewhich may be displayed by the digital mirror device. This is commonlyknown as interlaced to rolling field progressive scan conversion and isillustrated in FIG. 1. As can be seen from FIG. 1, the data in each pairof successive fields is combined to produce a frame of data which isthen displayed. Thus the “odd” and “even” fields of data from the firstframe are combined to produce the first frame to be displayed. Thesecond frame to be displayed comprises the “even” field of the firstframe, together with the “odd” field of the second frame. The thirdframe to be displayed comprises the data from the “odd” and “even”fields of the second frame. The fourth frame to be displayed comprisesthe data from the “even” field of the second frame and the “odd” fieldof the third frame, and so on. By such an arrangement a “smoothed” imageis produced.

Where such an interlaced scan video signal is used to address a digitalmirror device, because the pairs of successive fields are displayedsimultaneously rather than sequentially as in a cathode ray tube, in thecase of images of objects which have moved between the time of recordingthe two fields the time lapse between, subsequent fields in each framewill create a double image.

In order to overcome this problem of double images in a camera derivedsignal where there has been movement of the image between successivefields, it is known to convert the interlaced scan video signal, afterbeing digitized into pixel values for each mirror element of the digitalmirror device, providing interpolated lines of pixel values byinterpolating the missing lines from the most recently received fieldand then combining them with the most recently received field into acomplete frame of pixel values. Comparison of the interpolated fieldwith the field immediately prior to the most recent field may beemployed to establish the existence of motion between successive fieldsand hence can be used to determine which of the preceding andinterpolated fields are used to make up the complete frame. Thisconversion of fields to frames is known as “motion adaptive progressivescan conversion” and is illustrated schematically in FIG. 2 which showsthe interpolated fields used in such a progressive scan conversion wherethere has been movement of the image between successive fields.

(2) Description of Related Art

An example of the use of an interlaced scan video signal to address adigital mirror device after conversion to a progressive scan is shown inU.S. Pat. No. 5530482 in which a staggered mirror device pattern is usedto improve the perceived horizontal resolution of the display system.

EP-A-0740468 discloses a television receiver in which an interlace toprogressive scan conversion takes place in order to enable a digitalmirror device to display images represented by the input interlacedsignals. Interpolated fields are included to compensate for the inputdata which is designed for use with a scanning display, such as acathode ray tube.

Whilst, as can be seen from the prior art, it is possible to adaptinterlaced television signals for use by a progressively scanned spatiallight modulator such as a digital mirror device, particular problemsarise when the video signal is derived from a scanned film source. Suchscanning is typically performed by a telecine scanner which is used totransfer transparencies or films onto video tape by scanning thetransparency or each frame of the film with a point source of light,typically a cathode ray tube, in a raster pattern. The red, green andblue light passing through the transparency or film is detected by arespective photodetector, for example a photo multiplier for each of thethree primary colours, red, green and blue in combination withappropriate filters, so as to generate an analogue signal representativeof each frame of the film for each colour channel. The three colourchannel signals are then converted to the appropriate luminance andcolour difference signals for the relevant transmission standard. Theraster scan information for each film frame is separated onto an “odd”field containing all the odd numbered scan lines and an “even” fieldcontaining all the even numbered lines. Further, depending on thesetting of the telecine machine, each image frame may be transmitted“odd” field first or “even” field first.

International application WO-A-92/09172 discloses an interlaced videosignal derived from a film source using a telecine apparatus for usewith a display system in which the display device is a digital mirrordevice. The video signal is arranged to incorporate a number of flagseffective to denote that the video signal has been derived from a filmsource, and the position of the odd fields. Using this information, thedisplay system is able to create frames for display in which only fieldsof data derived from the same image frame are combined into frames anddisplayed. However, in practice, video signals derived from film sourcesusing, for example, a telecine apparatus do not incorporate such flagsas the video signals are designed for use with a variety of displaydevices in which interlaced scans do not present a problem.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a means for enablinga display apparatus using a display device such as a deformable mirrorarray which displays a full frame of information at every field intervalusing an interlaced video signal derived from a film source.

According to an aspect of the present invention there is provided adisplay apparatus including a spatial light modulator means forinputting an interlaced video signal produced by scanning successiveimage frames, the video signal comprising data signals representative ofthe successive image frames; means for determining from the data signalswhich signals have been derived from single frames of the scanned framesand producing signals representative of the frames; and a spatial lightmodulator drivable by said signals representative of the frames.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of embodiments of the present invention will now be describedby way of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic diagram illustrating interlaced scan toprogressive rolling field scan conversion as described above;

FIG. 2 is a schematic diagram illustrating interlaced scan to motionadaptive progressive scan conversion as described above;

FIG. 3 is a schematic diagram illustrating the production of aninterlaced video signal from a film source by a telecine scanner and theinput of such a video signal to a display apparatus in accordance withan embodiment of the invention;

FIG. 4 illustrates the combination of successive fields into thedisplayed frames in accordance with the first embodiment of the presentinvention;

FIG. 5 illustrates circuitry for producing a modified interlaced toprogressive scan conversion incorporated in a display apparatus inaccordance with a first embodiment of the present invention;

FIG. 6 illustrates further circuitry incorporated in a display apparatusin accordance with the first embodiment of the present invention fordisplaying the converted progressive scan data produced by the circuitryof FIG. 5 by a digital mirror device;

FIG. 7 is an overview of the optical system for the digital mirrordevices of FIG. 6;

FIG. 8 illustrates schematically circuitry for producing a modifiedinterlaced to progressive scan conversion incorporated in a displayapparatus in accordance with a second embodiment of the presentinvention;

FIG. 9 illustrates a 60 Hz NTSC transmission signal; and

FIG. 10 illustrates schematically circuitry for producing a modifiedinterlaced to progressive scan conversion incorporated in a displayapparatus in accordance with a third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 3 this Figure illustrates the production of aninterlaced video signal from original film stock by a telecine scanner,and the subsequent display of the images carried on the film stock by adigital mirror device. Region I represents the originating film stock,Region II represents the conversion by the telecine scanner of theinformation in the frames of the film to an interlaced scan videosignal, Region III represents the conversion of the interlaced scanvideo signal to a modified progressive scan signal in accordance with anembodiment of the invention, and Region IV represents the address of adigital mirror device by the modified progressive scan signal.

As illustrated in Region I of FIG. 3, the source material comprises acinematographic film 301 including a run of frames 303 of image data,only two frames being shown in the figure. The film 301 includes alongeach border alignment holes for use by the telecine scanner (not shown)in aligning the film with the cathode ray tube incorporated in thetelecine scanner.

As the cathode ray tube of the telecine scanner scans across each frame303 of the film 301, analogue signals representative of the successiveodd and even fields of data are produced as indicated in Region II ofFIG. 3. As explained above in relation to FIG. 2, in the conventionalinterlaced scan to progressive scan conversion or motion adaptiveprogressive scan conversion, successive pairs of fields of data arecombined to produce frames of data to be displayed. However, inaccordance with the embodiments of the present invention to bedescribed, and as also illustrated in FIG. 4 the display apparatus isarranged such that “odd” and “even” fields of data from each frame ofthe film are combined, whilst the intermediate frames produced bysuccessive “even” and “odd” fields from different frames are identifiedby the display system and not used. Digital data representative of eachframe is stored. The address system for the display device is thenarranged so as to display each frame of data twice.

The signal output of the telecine scanner is of conventional televisionsignal format and as indicated in Region II of FIG. 3 includessuccessive fields of analogue signals comprising successive “odd” and“even” fields of chrominance and luminance information derived from thesuccessive frames of the cinematographic film, together withconventional line synchronization signals at the end of the signal foreach scanned line and frame signals at the end of the signal for eachfield. In this particular example, the signal is designed for the PALsystem with the luminance and chrominance signals represented by YUVdata. The film 201 is scanned at a rate of 25 frames per second, witheach interlace field comprising 288 lines.

The form of the display apparatus including means for performing thesignal processing indicated in Regions III and IV of FIG. 3 will now bedescribed in more detail.

Turning now to FIG. 5, in the display apparatus forming the firstembodiment of the invention to be described, the interlaced YUV videosignal output of the telecine scanner with clock signals at the pixelsample rate is converted into red, green and blue primary colourchannels by separation unit 501, data within each colour channel beingentered into a respective analogue to digital converter 503, 505, 507 inorder to provide a digital signal representative of the required valuesof each of the pixels of the image to be displayed for each primarycolour. In an alternative arrangement, the separation into the threeprimary colour channels may be performed digitally after the YUV signalfrom the telecine scanner has been digitised. The three separate digitalsignal outputs from the analogue to digital converters 503, 505, 507within the three separate primary colour channels red, green and blueare entered into respective frame stores 509, 511, 513 each effective tostore three successive fields of data whilst being loaded with a fourthfield of data. Each frame store 509, 511, 513 is under the control of arespective page address system 515, 517, 519.

The apparatus is designed such that successive pairs of interlacedfields are combined into single frames of data, with pairs of fields notbeing derived from the same film stock frame 203 in FIG. 3 beingidentified and not displayed, thus avoiding the problems of the priorart systems. This is achieved as follows: As the leading field producedby the telecine scanner can be “odd” or “even” dependent on how thetelecine scanner has been set up, it is possible that “even” and “odd”fields of data from successive frames, for example “1 EVEN” and “2 ODD”may be combined rather than the required pairs of data “1 ODD” and “1EVEN”, or “2 ODD” and “2 EVEN” etc originating from the same film frame303. If the field dominance is such that fields of data from differentframe 303 of the film stock 301 are combined, the display system willdisplay an image of poorer characteristics than that obtained where thepairs of fields are derived from the same frame 303 of the film stock301. The display apparatus is provided with a manual field dominanceswitch 521 which enables the user to make a choice between the twopossible sets of combinations of successive fields, for example “1 ODD”and “1 EVEN”, or “1 EVEN” and “2 ODD” etc in order to achieve the bestprojected image. Operation of the manual field dominance switch 521causes a signal to be sent to the page address systems 515, 517, 519provided in respect of each colour channel. The signals produced by thepage address systems 515, 517, 519 inhibits the outputs by therespective frame stores 509, 511, 513 of the frame data corresponding toinvalid field combinations derived from different frames of the filmstock, whilst allowing the output of valid field combinations derivedfrom the same film frames.

Turning now to FIG. 6, this figure shows the circuitry for one colourchannel, the circuitry for the other two channels being identical. Theoutput of each frame store 509, 511, 513 is applied to a respectivegamma correction unit 601 effective to remove the gamma correctionsignal which is normally present in video signals for display on acathode ray tube. The output of each gamma correction unit 601 isapplied to a respective data formatting unit 603 effective to convertthe word serial video input into a format suitable for addressing adigital mirror device responsive to light within the particular colourchannel, including scaling the data to match the digital mirror devicemirror array configuration.

The data formatting unit 603 is arranged to address alternately twoframe stores 605, of which only one is illustrated in FIG. 6. Each framestore 605 in the address circuitry is arranged to store the video datafor each mirror element of the digital mirror device array and to supplythis data to the control electrodes of each mirror element within thedigital mirror device 609 via the driver circuit 607 under the controlof the sequencer 611.

The sequencer 611 is arranged to address the deformable mirror devicewith the data signals for each frame of data twice. If the film 201progresses through the telecine machine at a rate of 25 frames persecond, an output of 50 frames per second is thus produced, this doubleprojection technique giving a “film feel” quality to the projectedimage.

The mirror elements of each digital mirror device may each have theirown memory device or data latch effective to receive the input datasignal prior to the signals being applied to the mirror driveelectrodes. Alternatively groups of the mirror elements in the digitalmirror device array, for example horizontal lines of the mirrorelements, may be connected to a common memory device in which case it isnecessary to apply reset signals (in this example) to the vertical rowsof mirror devices in order to identify the correct mirror devices to beaddressed by the data signals.

Each sequencer 611 may, if required, be arranged to apply appropriatereset signals to the electrodes of the respective digital mirror device609 to enable the appropriate data signals to be applied to the chosenmirror elements within the digital mirror device. Whilst the frame store605 is supplying data to the associated digital mirror array, the otherframe store (not shown) is receiving fresh video data from the dataformatting unit 603.

Referring now also to FIG. 7, each digital mirror device is illuminatedwith light of the appropriate primary colour red, green or blue to matchthe address signals produced from the appropriate frame store 605. Thisis preferably by means of a white light source 701, for example, a Xenonarc lamp, the light from which is directed through a series of colourselective dichroic mirrors 703, 705 to produce light of the appropriatecolour on the red, green and blue digital mirror arrays 707, 709, 711.The spatially modulated light from the three arrays 707, 709, 711 isrecombined at the dichroic mirrors 703, 705 and projected through aprojection lens 713 onto a display surface 715. It will be appreciatedthat the optical arrangement shown in FIG. 7 merely illustrates theprinciple of operation of a projection system using the displayapparatus to project an image on the display surface 715 and omits manyoptical features, for example beam shaping arrangements and a reflectorin the green channel for equalising the number of reflections which thespatially modulated light undergoes.

As the digital mirror array is a binary device, i.e. the light reflectedfrom each mirror to the projection screen is only “on” or “off” in orderto display grey scale the mirrors of the device are switched “on” fordifferent lengths of time corresponding to the light level to bedisplayed as signified by the input video signal. The way in which thevarious mirrors are turned “on” for different lengths of time isdescribed, for example in our co-pending International Application WO94/09473.

Whilst the above embodiment illustrates the general principle of theinvention, it will be appreciated that the intervention of an operatorto effect the switching of the manual field dominance switch 521 isinconvenient. FIG. 8 illustrates an embodiment of the invention in whichthe selection of the required combinations of fields from the inputvideo signal is performed automatically by detecting motion betweenadjacent fields, using such motion to identify invalid combinations ofpairs of fields which have been derived from different frames 303 of thefilm stock 301, and inhibiting display of images from the invalidcombinations.

FIG. 8 illustrates the circuitry for only the green channel of the red,green and blue colour channels, equivalent circuitry being provided forthe other two channels. As in the first embodiment, each of the red,blue and green colour channels of the input interlaced video signaloutput of the telecine scanner is applied to a respective analogue todigital converters 801 together with pixel sample clock signals, thedigitised signals being applied to a respective frame store 803.However, in this embodiment pairs of fields originating from differentframes 303 of the film stock 301 in FIG. 3 are identified, and preventedfrom being combined as will now be explained.

The output of the analogue to digital converter 801 is also applied to aline delay circuit 805, a line interpolator circuit 807 and a fielddelay circuit 809. An output from the line delay circuit 805 is alsoapplied to the line interpolator circuit 807 which is effective toproduce an interpolated line of data between the current line and theprevious line of the same field of data. Thus, if the field is an “even”field, line numbers 2, 4, 6 etc being present, the line interpolator iseffective to produce interpolated values for the “odd” field lines 3, 5etc by forming averages of the pixel values for corresponding pixels insuccessive even lines of the input “even” field.

A motion detector 811 is effective to compare the values of the pixelsin the interpolated lines with the values of the lines for the previousfield of data. Thus, if for example, “odd” interpolated lines have beenproduced by the current “even” field, data from corresponding pixels inthe interpolated lines are compared with the previous “odd” field dataoutput from the field delay circuit 809. Likewise “even” interpolateddata may be produced from a current “odd” field, and compared with theprevious “even” field. By this means it is possible to determine whetherthere have been any changes between the interpolated lines of datacorresponding to the current field and the lines of the previous field,such changes indicating that the fields have originated from differentframes 303 of the film stock 301.

As in the first embodiment, enabling signals are input from the motiondetector 811 to a page address circuit 813 for the frame store 803. Thepage address circuitry 813 is used to address the appropriate data inthe store 803 such that the frame store 803 outputs the requiredcombination of two fields of data from the same film frame 303 of theoriginal film stock in order to provide a full frame of data to thedigital mirror device 609. The further processing of the output of theframe store 803 is then carried out in similar manner to FIG. 6.

Thus by use of the circuitry illustrated in FIG. 8 it is possible todiscriminate automatically between the sequences of “odd” and “even”fields of data in the interlaced video signal output of the telecinemachine.

Turning now to FIGS. 9 and 10, this third embodiment of the invention tobe described is an adaptation of the second embodiment but isadditionally arranged to deal with the output of a telecine scannerwhich has been used to provide an output suitable for the American NTSC60frames per second television standard. In order to produce thisstandard from a normal cinematographic film which has been shot at 25frames per second, the telecine scanner is arranged to repeat everyfifth field to produce an interlaced output at a 60 Hz vertical displayrate. This is illustrated in FIG. 9 which shows the correspondencebetween the fields of the 60 Hz NTSC interlaced video signal with the 50Hz interlaced video signal as has previously been described, and theframes of the film stock 203. As can be seen, the first “odd” frame O₁is repeated in this particular example, followed by a repeat of thethird “even” field E₃. As three fields are transmitted corresponding tothe first frame of the film stock, followed by two fields correspondingto the next frame of the film stock, this is commonly referred to as 3:2film pull down in the telecine.

Turning now to FIG. 10 in which again the circuitry for one colourchannel is shown, in order to deal with such video signal input, fieldsof data which are repeated are identified and not displayed by thedigital mirror devices.

FIG. 10 is an adaptation of the circuit shown in FIG. 8 and thuscorresponding features are correspondingly labelled. However, inaddition to the circuit of FIG. 8, the circuit of FIG. 10 includes afurther field delay circuit 1001, a further motion detector circuit1003, a times five multiplier circuit 1007 and a divide by six dividercircuit 1009.

As in the previous embodiment, the line interpolator 807 is arranged toproduce spatially interpolated lines to enable comparison withcorresponding lines in the preceding field to determine field dominanceand thus prevent combinations of fields originating from differentframes 303 of the original film stock 301. The second field delaycircuit 1001 and motion detector 1003 enables comparison of a two fielddelayed field of data with the present field of data to determinewhether the field has been repeated.

If the motion detector 1003 detects no motion between the current fieldand the twice delayed field, then the current field is discarded.Otherwise the circuit operates as for the second embodiment describedwith reference to FIG. 8.

It will be appreciated that the only valid combination of fields of datawill be produced when the motion detector 811 detects no differencebetween the interpolated lines of the current field and the previousfield, and the motion detector 1003 detects a difference between thecurrent field and the twice delayed field. The times five multiplier1007 and divide by six divider 1009 produces the required 50 Hz inputsignal to the page address system 813 for clocking the frame store 803.The output of the frame store 803 is applied to the digital mirrordevice address circuitry 601 to 611 of FIG. 6 as described in relationto the first and second embodiments.

It will be appreciated that whilst the apparatus described above isdescribed in relation to a single colour channel, in an apparatus inwhich a single digital mirror device is provided for each primary colourchannel the invention is also applicable to a monochrome system or to adisplay apparatus incorporating a colour wheel in which red, green andblue data is applied sequentially to the same digital mirror devicearray. Such a colour wheel may be implemented electronically by use ofone or more auxiliary digital mirror devices used as colour switches asdescribed in our co-pending International application WO97/20242.

It will also be appreciated that the apparatus of FIG. 5 incorporating amanual field dominance switch can be adapted for use with an incoming 60Hz NTSC signal in similar manner to that of FIG. 10, by including amotion detector for identifying fields which have been repeated, andsuppressing such fields.

What is claimed is:
 1. A display apparatus comprising: means forinputting an interlaced video signal comprising data signalsrepresentative of successive fields of image data; a spatial lightmodulator system electrically addressable by signals representative ofsaid video signal; means for determining from said data signals whethersuccessive pairs of fields of image data are derived from respectivesuccessive single frames of the image frames; and address meanseffective to address said spatial light modulator system only withsignals representative of said pairs of fields of image data which aredetermined to be derived from said respective successive single framessuch that the spatial light modulator system produces successive imagesrepresentative of respective successive image frames, wherein said meansfor determining comprises a manually operable field dominance switchmeans operative to select pairs of fields for addressing the spatiallight modulator system during each frame interval dependent on anobserver's perception of the image produced by the spatial lightmodulator system.
 2. A display apparatus according to claim 1, in whichsaid interlaced video signal includes periodic repeated fields, whereinsaid determining means is arranged to determine image data correspondingto pairs of repeated fields, and said address means is arranged suchthat the spatial light modulator system is addressed with signalsrepresentative of only one of each pair of repeated fields.
 3. A displayapparatus comprising: means for inputting an interlaced video signalcomprising data signals representative of successive fields of imagedata; a spatial light modulator system electrically addressable bysignals representative of said video signal; means for determining fromsaid data signals whether successive pairs of fields of image data arederived from respective successive single frames of the image frames;address means effective to address said spatial light modulator systemonly with signals representative of said pairs of fields of image datawhich are determined to be derived from said respective successivesingle frames such that the spatial light modulator system producessuccessive images representative of respective successive image frames;wherein said means for determining comprises a motion detection circuitcomprising: (i) means for inputting successive portions of data,successive pluralities of the portions together forming successive onesof said plurality of successive fields of image data; (ii) means forforming successive interpolated portions of each field of image databased on the previous and current portions of data; and (iii) means forcomparing each interpolated portion of successive fields of data withthe corresponding portion of data in the previous field of data todetermine whether motion has occurred between the compared portions ofdata, thereby determining whether the current field and previous fieldare derived from a single image frame.
 4. A display apparatus accordingto claim 3, wherein said portions are lines of image data.
 5. A displayapparatus according to claim 3, in which said interlaced video signalincludes periodic repeated fields, wherein said determining means isarranged to determine image data corresponding to pairs of repeatedfields, and said address means is arranged such that the spatial lightmodulator system is addressed with signals representative of only one ofeach pair of repeated fields.
 6. A display apparatus according to claim5, wherein said motion detection circuit further comprises: means forcomparing each current field of data with a second previous field ofdata; and means for causing the spatial light modulator system toproduce an image from the current field of data only when theinterpolated portions show no motion with respect to the portion of datafrom the previous field and the current and second previous fields showmotion.
 7. A display apparatus according to claim 5, wherein theinterlaced signal is a 60 Hz 3:2 pull-down signal, and the apparatusincludes means for clocking the address means such that the spatiallight modulator system is arranged to produce successive images at 50Hz.
 8. A display apparatus according to claim 1, or 3, wherein saidaddress means is arranged to cause said spatial light modulator systemto produce an image representative of each frame of data at least twice.9. A display apparatus according to claim 1, or 3, wherein the spatiallight modulator system comprises a digital mirror device.
 10. A displayapparatus according to claim 1, or 3, wherein a spatial light modulatorsystem and an associated address means is provided in respect of eachone of several colour channels.
 11. A display apparatus according toclaim 1, or 3, including means for supplying image data representativeof different colours sequentially to the same spatial light modulatorsystem.
 12. A display apparatus according to claim 1, or 3, in whichsaid interlaced video signal is produced by a telecine apparatus.
 13. Adisplay system including a display apparatus according to claim 1 or 3and a display surface.
 14. A display method using an electricallyaddressable spatial light modulator system, the method comprising thesteps of: inputting an interlaced video signal comprising signalsrepresentative of successive fields of image data; determiningsuccessive pairs of fields of image data derived from respectivesuccessive single frames of the image frames; and causing an addressmeans to address said spatial light modulator system only with signalsrepresentative of said pairs of fields of image data derived fromrespective successive single frames of the image frames to producesuccessive images representative of respective successive image frames;wherein said determining step comprises operating a manual fielddominance switch effective to select pairs of fields derived from asingle image frame dependent on an observer's perception of the imageproduced by the spatial light modulator system.
 15. A display methodaccording to claim 14, in which said interlaced video signal includesperiodic repeated fields and including the step of determining imagedata corresponding to pairs of repeated fields, and addressing thespatial light modulator system with signals representative of only oneof each pair of repeated fields.
 16. A display method using anelectrically addressable spatial light modulator system, the methodcomprising the steps of: inputting an interlaced video signal comprisingsignals representative of successive fields of image data; determiningsuccessive pairs of fields of image data derived from respectivesuccessive single frames of the image frames; and causing an addressmeans to address said spatial light modulator system only with signalsrepresentative of said pairs of fields of image data derived fromrespective successive single frames of the image frames to producesuccessive images representative of respective successive image frames;wherein said determining step comprises: (i) inputting successiveportions of data, successive pluralities of the portions togetherforming successive ones of said plurality of successive fields of imagedata; (ii) forming successive interpolated portions of each field ofdata based on the previous and current corresponding portions of data;and (iii) comparing each interpolated portion of a field of data withthe corresponding portion of data in the previous field to determinewhether motion has occurred between the compared portions of data,thereby determining whether the current field and previous field arederived from a single image frame.
 17. A display method according toclaim 16, wherein said portions are lines of image data.
 18. A displaymethod according to claim 16, in which said interlaced video signalincludes periodic repeated fields and including the step of determiningimage data corresponding to pairs of repeated fields, and addressing thespatial light modulator system with signals representative of only oneof each pair of repeated fields.
 19. A display method according to claim18, wherein said determining step comprises: comparing each currentfield of data with a second previous field of data; and causing thespatial light modulator system to produce an image from the currentfield of data only when the interpolated portions show no motion withrespect to the portion of data from the previous field and the currentand second previous fields show motion.
 20. A display method accordingto claim in 18, which the interlaced video signal is a 60 Hz 3:2pull-down signal, and the method includes the steps of clocking theaddress means to cause the spatial light modulator system to producesuccessive images at 50 Hz.
 21. A display method according to claim 14or 16, wherein said addressing step is arranged to cause said spatiallight modulator system to produce an image representative of each frameof data at least twice.
 22. A display method according to claim 14 or16, wherein the spatial light modulator system is a digital mirrordevice.
 23. A display method according to claim 14 or 16, wherein aspatial light modulator system is provided in respect of each one ofseveral colour channels.
 24. A display method according to claim 14 or16, in which image data representative of different colours is suppliedsequentially to the spatial light modulator system.